The object of our study is to provide a coherent basis for the understanding of the electromagnetic properties and biochemical reactivity of cytochrome P450. The reactive cycle of P450s is well characterized and involves four stable states of the enzyme and a fifth, reactive state which carries out the oxidation. Each of the stable states has a number of characteristic electromagnetic properties which can be directly related to the immediate environment around the heme unit as the protein proceeds through the reaction cycle. Using the method of quantum chemistry, we propose to characterize the conformation, electronic structure and spin distribution of each of the stable states of the heme unit. The results will be used to calculate electromagnetic properties which can then be compared to experiment. In this way a realistic model for each of the four stages will be obtained which is consistent with experimental behavior and which furnishes a more detailed description of the active site than can be obtained from the experiments alone.